from math import sqrt

def main():

    x1, y1, x2, y2 = map(float, input().split())
    print(sqrt(abs(x2-x1)**2 + abs(y2-y1)**2))


main() from math import sqrt def main():

    x1, y1, x2, y2 = map(float, input().split())
    print(sqrt(abs(x2-x1)**2 + abs(y2-y1)**2)) main x1, y1, x2, y2 = map(float, input().split()) x1 map(float, input().split()) map float input().split() ().split () input split y1 x2 y2 print(sqrt(abs(x2-x1)**2 + abs(y2-y1)**2)) print sqrt(abs(x2-x1)**2 + abs(y2-y1)**2) sqrt abs(x2-x1)**2 + abs(y2-y1)**2 abs(x2-x1)**2 abs(x2-x1) abs x2-x1 x2 x1 2 abs(y2-y1)**2 abs(y2-y1) abs y2-y1 y2 y1 2 main() main def main():

    x1, y1, x2, y2 = map(float, input().split())
    print(sqrt(abs(x2-x1)**2 + abs(y2-y1)**2)) def main():

    x1, y1, x2, y2 = map(float, input().split())
    print(sqrt(abs(x2-x1)**2 + abs(y2-y1)**2)) main
from math import sqrt

def main():

    x1, y1, x2, y2 = map(float, input().split())
    print(sqrt(abs(x2-x1)**2 + abs(y2-y1)**2))


main()